Geo

A collection of GIS functions. Handles conversions to and from WKT, WKB, and GeoJSON for the following geometries:

• Point
• LineString
• Polygon
• MultiPoint
• MulitLineString
• MultiPolygon
• GeometryCollection

Also includes an encoder, decoder, and formatter for using PostGIS data types with Postgrex

defp deps do
  [{:geo, "~> 0.10.1"}]
end

Documentation

Examples

• Encode and decode WKT and EWKT

  iex(1)> point = Geo.WKT.decode("POINT(30 -90)")
  %Geo.Geometry{type: :point, coordinates: [30, -90], srid: nil}
  
  iex(2)> Geo.WKT.encode(point)
  "POINT(30 -90)"
  
  iex(3)> point = Geo.WKT.decode("SRID=4326;POINT(30 -90)")
  %Geo.Geometry{type: :point, coordinates: [30, -90], srid: 4326}

• Encode and decode WKB and EWKB

  iex(1)> point = Geo.WKB.decode("0101000000000000000000F03F000000000000F03F")
  %Geo.Geometry{ type: :point, coordinates: [1.0, 1.0], srid: nil }
  
  iex(2)> Geo.WKB.encode(point)
  "00000000013FF00000000000003FF0000000000000"
  
  iex(3)> point = Geo.WKB.decode("0101000020E61000009EFB613A637B4240CF2C0950D3735EC0")
  %Geo.Geometry{ type: :point, coordinates: [36.9639657, -121.8097725], srid: 4326 }
  
  iex(4)> Geo.WKB.encode(point)
  "0020000001000010E640427B633A61FB9EC05E73D350092CCF"

• Encode and decode GeoJSON

  iex(1)> point = Geo.JSON.decode("{ \"type\": \"Point\", \"coordinates\": [100.0, 0.0] }")
  %Geo.Geometry{ type: :point, coordinates: [100.0, 0.0], srid: nil }
  
  iex(2)> Geo.JSON.encode(point)
  "{\"type\":\"Point\",\"coordinates\":[100.0,0.0]}"

• Encoder, Decoder, and Formatter to be used with Postgrex for PostGIS data types

  opts = [hostname: "localhost", username: "postgres", database: "geo_postgrex_test",
  encoder: &Geo.PostGIS.encoder/3, decoder: &Geo.PostGIS.decoder/4,
  formatter: &Geo.PostGIS.formatter/1 ]
  
  [hostname: "localhost", username: "postgres", database: "geo_postgrex_test",
   encoder: &Geo.PostGIS.encoder/3, decoder: &Geo.PostGIS.decoder/4,
   formatter: &Geo.PostGIS.formatter/1]
  
  {:ok, pid} = Postgrex.Connection.start_link(opts)
  {:ok, #PID<0.115.0>}
  
  geo = %Geo.Geometry{type: :point, coordinates: [30, -90], srid: 4326}
  %Geo.Geometry{coordinates: [30, -90], srid: 4326, type: :point}
  
  {:ok, _} = Postgrex.Connection.query(pid, "CREATE TABLE point_test (id int, geom geometry(Point, 4326))")
  {:ok, %Postgrex.Result{columns: nil, command: :create_table, num_rows: 0, rows: nil}}
  
  {:ok, _} = Postgrex.Connection.query(pid, "INSERT INTO point_test VALUES ($1, $2)", [42, geo])
  {:ok, %Postgrex.Result{columns: nil, command: :insert, num_rows: 1, rows: nil}}
  
  Postgrex.Connection.query(pid, "SELECT * FROM point_test")
  {:ok, %Postgrex.Result{columns: ["id", "geom"], command: :select, num_rows: 1,
  rows: [{42, %Geo.Geometry{coordinates: [30.0, -90.0], srid: 4326, type: :point}}]}}

• Can now be used with Ecto as well

  
  #Add encoder, decoder, and formatter to your repo config
  config :thanks, Repo,
    database: "geo_postgrex_test",
    username: "postgres",
    password: "postgres",
    hostname: "localhost",
    encoder:  &Geo.PostGIS.encoder/3, 
    decoder:  &Geo.PostGIS.decoder/4,
    formatter: &Geo.PostGIS.formatter/1
  
  
  #Create a model
  defmodule Test do
    use Ecto.Model
  
    schema "test" do
      field :name,           :string
      field :geom,           Geo.Geometry
    end
  end
  
  #Geometry columns can be created in migrations too
  defmodule Repo.Migrations.Init do
    use Ecto.Migration
  
    def up do
      create table(:test) do
        add :name,     :string
        add :geom,     :geometry
      end
    end
  
    def down do
      drop table(:test)
    end
  end